In the interior of extrusion machines of the industry processing rubber and synthetic materials, the extrudable material or extrudate is under pressures, in particular at the end of the passage through the extrusion machine where the material is disintegrated and in a flowable state. At this place frequently a filter, also referred to as a strainer, is disposed in the path of the extrudate in order to remove parts and foreign bodies which cannot be disintegrated from the flow of the extrudate, conventionally directly following the extrusion device, which can be a screw extruder, ram extruder, toothed wheel or other extruder, before the extrudate leaves the discharge head disposed at the end of the extrusion device.
The strainers must be cleaned from time to time. In order not to interrupt the production operation for the cleaning, strainer-changing devices were developed which are installed in the extrusion system for example, between extruder and discharge head. These comprise discrete strainer cassettes or a slider with at least two strainers and means for a rapid displacement of this strainer cassette or this slider into their operating positions. Due to the high pressures occurring at the site of the strainer, problems are encountered to attain "perfect" sealing during operation with high contact pressures in the region of the seal, but to decrease briefly the high contact pressures for the displacement of the slider so far that the slider or the strainer cassettes without damage and without damaging the seal used can be slid in order to make them effective again immediately after the displacement of the slider with the strainers or the strainer cassettes.
Also, for the reason of not having to interrupt the production operation or only extremely briefly, similar apparatus are used in the discharge head region as tool changers.
Technology has developed a number of options of which, however, none is fully satisfactory.
In DE 3043217 C2, two meshing rings are hydraulically displaced and pressed against the slider. Since here an annular cylinder comprising two concentrically disposed corrugated pipes causes the hydraulic displacement, and the attainable contact pressures are not sufficient for many applications since the strength of the corrugated pipes fabricated of very thin material is highly limited.
In DE 1919269, the contact pressing takes place by means of a ring which is impressed upon by piston rods, acting obliquely upon it, of small hydraulic cylinders. The sealing of the cylindrical inner circumferential surface of this ring and the occurring transverse forces here represent problems.
In DE 1729396, the compacting pressure is not exerted onto annular surfaces but rather only on two opposing sites via wedge surfaces.
In DE 19615679, A1 mechanical displacement is achieved not with hydraulic forces but rather by rotation of a pressing ring provided with outer threads in an inner threading. High contact pressures, and thus sealing pressures, cannot be attained due to the high frictions and locally unequal contact pressing due to thread tolerances. The resetting with defined residual pressure is also not readily possible.
The invention avoids the disadvantages of the prior art. It is the task of the invention to create with simple means a unique sealing device which seals, for example, an extrusion machine even at very high pressures and yet is readily relieved of load if a machine part is to be displaced relative to the other.